Ethernet as a Control Network
29 April to 1 May
Ethernet’s worldwide acceptance in industrial and office environments has
created an eagerness to expand its responsibilities on the plant floor. Ethernet is
widely used for information (office, Human Machine Interface (HMI), controller
programming, etc.) communications today. The network’s performance
capabilities make it ideal for tasks such as data monitoring and program
maintenance. However, many predict that recent technological advancements in
Ethernet, and the emerging Fast Ethernet technology, will also enable it to handle
mission-critical control responsibilities currently being managed by existing
industrial automation networks. Meanwhile, others contend that Ethernet has a
long way to go before it can assume an expanded role in the manufacturing
Ethernet technology brings availability, familiarity, and possible cost benefits.
Until recently, however, creating an industrial control system by using Ethernet at
the device (I/O) network was not feasible due to a number of factors, including
Ethernets lack of determinism, the need for interoperability among devices,
security concerns, etc.
Determinism is the ability to predict when information will be delivered. To
guarantee this, an industrial control network must provide scheduled bandwidth
(or time slots) that are reserved for time-critical data transfer. Communication
over Ethernet, however, is based upon collision detection. If a device attempts to
send a message, and that message collides with another message on the
Ethernet media, the device backs off and waits to transmit. Thus cannot
Recent advances in switch technology have now enabled Ethernet to approach
determinism. Switches, unlike traditional bridges and hubs, reduce traffic
between the devices attached to their ports. Moreover, the IEEE 802.3 Standard
provides for standardized full-duplex operation, which gives a single node - in a
point-to-point connection to the switch - full wire concentration. As a result, full-
duplex switched Ethernet networks are theoretically able to avoid collisions.
The requirement for device interoperability, the ability of products from different
control vendors to communicate with each other, has been answered by a
plethora of industrial communication protocol ‘standards’ from a wide community
of automation vendor groups.
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Ethernet OSI Model
All installed Ethernet networks support one or more communication protocols that
run on top of Ethernet and provide sophisticated data transfer and network
management functionality. The communications protocol determines what level
of functionality is supported by the network, what types of devices may be
connected to the network, and how devices interoperate on the network.
TCP/IP (transmission control protocol/internet protocol) is the communications
protocol of the Internet. TCP/IP is a layered protocol that can be mapped
approximately to the OSI (Open System Interconnection) seven-layer network
model shown in the following figure. The OSI model represents the components
of a standard open network architecture.
In this model, Ethernet represents Layers 1 (Physical) and 2 (Data Link). The
Internet Protocol (IP) maps to Layer 3 (Network). The TCP and UDP transports
map to Layer 4 (Transport). The TCP/IP protocol suite has no specific mapping
to Layers 5 and 6 of the model. The user services commonly associated with
TCP/IP networks map to Layer 7 (Application).
Each layer of the OSI model uses the services provided by the layer immediately
below it. For example, when a TCP connection needs to send a packet of data to
another device over Ethernet, it passes the packet to IP for transmission. IP then
handles the interface to Ethernet and ensures that the packet gets transmitted
onto the Ethernet network to the destination device. On the receiving end, the IP
layer receives the packet from the Ethernet interface, and passes it to the
appropriate TCP connection within the receiver.
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The topology, or physical configuration, of the original Ethernet networks was
primarily a multi-drop bus topology. With a bus topology every device on the
network can send data at any (same) time. All devices share the same logical
medium. As more devices are added to the network, bus contention increases.
In addition, bus-based designs are not indefinitely expandable due to increased
propagation delay when bus length is increased.
The emergence of repeater hubs and active switches enabled Ethernet networks
to be configured in a star topology, where the hub or switch acts as a network
concentrator for connecting multiple devices or Ethernet network segments.
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This is the most common topology found in new Ethernet installations today. The
hub/switch and its attached devices and segments may comprise the entire
Ethernet network, as would be typical in a small office environment. Or, the
hub/switch may be linked to another hub/switch, or to a fiber-optic backbone that
spans a building or campus, with hubs or switches connected to the backbone at
various points using uplink ports. The original Ethernet specifications described
a physical network layer running at 10 Mbit/sec. More recent developments in
Ethernet technology include Fast Ethernet (running at 100 Mbps/second) and
Data Link Layer
The Data Link Layer uses CSMA/CD (carrier sense multiple access/collision
detection) to manage bus contention for the network. A collision occurs when
two or more devices attempt to transmit at the same time. Each of the colliding
devices must then backoff and attempt to gain access to the wire according to
the CSMA/CD arbitration mechanism. Note that a collision is not an event to be
avoided, but simply a mechanism to allocate shared bandwidth for stations which
want to send data at the same time. The resolution occurs very quickly. The
station almost immediately aborts the transmission, gets off the channel, and
retransmits the frame after a random backoff time. Very little channel time is
wasted for the backoff as compared to valid data transmission times. The first
range of backoff time is 0...51.2us. An increase of the number of collisions on an
Ethernet is therefore not necessarily indicative of a problem, but only an
indication that there is more offered load.
Because it is impossible to predict the amount of time required for all colliding
devices to successfully complete their message transmission, the CSMA/CD
mechanism and its performance consequences has earned Ethernet its
reputation for being non-deterministic. However, depending upon the used
bandwidth of the network, data updates are still processed in a fast (milliseconds)
time frame. For example, an update may occur after 20ms, the next after 26ms,
the next after 23ms, etc., instead of exactly every 25ms. And if the updates are
required only every 50ms, the network is effectively deterministic for this
The use of Fast Ethernet can also provide a noticeable improvement over 10
Mbit Ethernet in the area of collision recovery. The backoff times for 100 Mbit
Ethernet are 1/10th of those for 10 Mbit Ethernet. On a loaded network where
collisions are an issue, 100 Mbit Ethernet will show noticeably better performance
than 10 Mbit Ethernet. In addition, a 100 Mbit Ethernet network is able to handle
a larger offered load than a 10 Mbit Ethernet network before collisions become
an issue. Coupled with Star topologies and the use of full duplex active switches
most of the collisions on an Ethernet Network can be eliminated.
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Gigabit Ethernet is an emerging technology defined in IEEE specification 802.3z.
It is basically Ethernet operating at 1000 Mbits/second (1Gigabit/sec). It is 100
times as fast as the original Ethernet, and 10 times as fast as Fast Ethernet. Like
those technologies, it uses the frame format, addressing scheme and CSMA/CD
mechanism described in the original 802.3 specifications. Gigabit Ethernet is
Ethernet. It is designed to run over both fiber and copper media. Gigabit
Ethernet at this time is primarily targeted for use as an enterprise-wide backbone.
It is likely that for at least the near future, the cost of this technology will preclude
its use down to the level of individual workstations, printers and other Ethernet
Ethernet provides only the Physical and (Data) Link layers seen at the bottom of
the OSI model. For this reason, all Ethernet networks support upper layer
protocols that run on top of it, providing sophisticated data transfer and network
management functionality. The Network layer provides the internetworking
protocol for the communications session.
IP (Internet Protocol) provides the routing mechanism. TCP/IP is a routable
protocol, which means that all messages contain not only the address of the
destination station, but the address of a destination network. This allows TCP/IP
messages to be sent to multiple networks within an organization or around the
world, hence its use in the business world and in the worldwide Internet. Every
client and server in a TCP/IP network requires an IP address, which is either
permanently assigned or dynamically assigned at startup.
The transports supported by the TCP/IP protocol suite are TCP (Transmission
Control Protocol) and UDP (User Datagram Protocol). They both map to the
Transport Layer of the OSI model.
TCP is a connection-oriented transport that provides reliable transmission of data
from one device to another. Once a TCP connection is established between two
devices, TCP handles fragmentation and re-assembly of message packets,
detects failures, performs retries, and generally provides a high quality of service
between the two devices. TCP guarantees the data will get from one device to
the other if it is possible. If the transmission fails for any reason, TCP ensures
that the applications on both ends of the TCP connection know it. TCP presents
data to the application layer above it in the form of a continuous byte stream.
The receiving application must be capable of recognizing any message delimiters
that might be embedded in the byte stream by the transmitting application. TCP
works only in unicast (point-to-point) mode, and is used by applications such as
FTP (File Transfer Protocol), HTTP (Web Server), and Telnet (terminal
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emulation). In an industrial automation application, TCP would typically be used
to download ladder programs between a workstation and a controller, for HMI
devices that read or write controller data tables, or for peer-to-peer messaging
between two controllers.
UDP is a much simpler transport protocol. It is connectionless and provides a
very simple capability to send datagrams between two devices. UDP is used by
applications that implement their own handshaking between two devices and only
want a minimal transport service. UDP is smaller, simpler, and faster than TCP
due to its minimal capabilities and use of resources. UDP can operate in unicast,
multicast or broadcast mode. In an industrial automation application, UDP would
typically be used for network management functions, applications that do not
require reliable data transmission or applications that are willing to implement
their own reliability scheme, such as flash memory programming of network
In order to provide interoperability among devices a common Application layer is
needed. It is this upper layer’s protocols that determines the level of functionality
a network supports, which devices may connect to the network, and how devices
interoperate on the network. Ethernet can only be as efficient as the network
whose upper-level protocols it uses.
The TCP protocol suite provides a set of services that two devices use to share
data. However, TCP does not guarantee these devices can communicate
effectively, if at all. It only guarantees that messages can be transferred between
the two devices. A common language is still needed for communication. For an
industrial version of Ethernet that language is a universal Application layer.
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Example of an Industrial Automation (Control) Protocol
EtherNet/IP is an industrialized extension of Ethernet TCP/IP which uses an
approach called “TCP/IP encapsulation” to apply a common application layer
over Ethernet. TCP/IP encapsulation allows a device node to encapsulate a
message as the data portion in an Ethernet message. The node then sends the
message - TCP/IP protocol with the message inside - to an Ethernet
communication chip (the Link layer). The standard application layer makes
interoperability and interchangeability of industrial automation and control devices
on Ethernet a reality for automation applications.
EtherNet/IP uses TCP/IP to send explicit messages - those in which the data field
carries both protocol information and instructions for service performance. With
explicit messaging, nodes must interpret each message, execute the requested
task, and generate responses. These types of messages are used for device
configuration and data collection, and are highly variable in both size and
frequency. In the industrial environment, TCP/IP is typically used to download
ladder programs between a workstation and a controller, for HMI devices that
read or write controller data tables, or for peer-to-peer messaging between two
For control (real-time) messaging, EtherNet/IP employs the User Datagram
Protocol/Internet Protocol (UDP/IP), which can multicast (i.e., broadcast) and
send implicit (real time) messages. The data field contains no protocol
information, only real-time I/O data. The application layer CIP takes care of
monitoring the UDP packet. The meaning of the data is predefined at the time
the connection is established, and therefore processing time in the node is
minimized during runtime. UDP messages are low overhead, short, and provide
the required, time-critical performance needed for control.
By using both TCP/IP and UDP/IP protocols to encapsulate networked
messages, both real-time I/O and explicit messaging can occur. EtherNet/IP
provides Ethernet users with real-time I/O, device-configuration, and diagnostic
capabilities, along with interoperability and interchangeability.
The Application layer used by EtherNet/IP (called CIP protocol) provides the
control functionality to TCP, IP and UDP. CIP handles handshaking at the
application level. It supports a common object library, device profiles, control
services, and routing. These objects and profiles make it possible for plug-and-
play interoperability among complex devices from multiple vendors. The object
definitions are rigorous and support real-time I/O control, configuration, and data
collection over the same network.
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CIP uses the “producer/consumer” (also called publish and subscribe) networking
model, replacing the old source/destination (master/slave) model. The
producer/consumer model contains all source/destination capabilities plus
additional capabilities for improved efficiency. In the source/destination model,
the source communicates with each destination, one at a time. Real time data
must be adjusted to maintain accuracy as communication takes place with each
source, one at a time. Some of the destinations may not need the information, so
that effort is wasted. Moreover, the delivery time changes with the number of
In the producer/consumer model one producer broadcasts (multicasts) the data
once to all the consumers. All consumers see the data simultaneously, and may
choose whether to consume (receive) the data or not. Delivery time is consistent
and bandwidth usage is optimized, no matter how many consumers there are.
Bandwidth optimization is especially important on Ethernet, where the amount of
data on the wire determines the number of collisions.
In addition to multicast data consumption, the producer/consumer model provides
for change-of-state and cyclic I/O. With change-of-state (event-driven), a sensor
produces data only when the object is present. Cyclic (time-driven) I/O can be
used for scheduled data transmission.
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Evolution of Switches
Bridges and Routers
The original Ethernet topology was a multi-drop bus architecture. With this
architecture, bridges and routers are used to reduce transmission time and
increase overall performance. Bridges are multi-port devices that connect
network segments that use different physical media. Bridges also monitor
network traffic, building and maintaining internal tables that list the port on which
each Ethernet address resides. When a bridge receives a packet destined for a
particular address, the bridge retransmits the packet only on the port at which the
device resides. Each port on a bridge represents a separate collision domain. A
router is a device that forwards traffic between networks based on network layer
information in the data and on routing tables it maintains. The router builds up a
logical picture of the overall network in its routing tables, and then uses this
information to choose the best path for forwarding network traffic.
Bridges and routers have similar bus-based architectures that function on shared
media. Data is received into a buffer and examined prior to forwarding. Multiple
segment contention is necessary for access to the bus. Bridges and routers also
have relatively high latencies (the time between initiating a request for data and
the beginning of the actual data transfer).
A hub (also called a “repeater hub”) is a common wiring point for star-topology
networks. Hubs have multiple ports to attach the different cable runs. Some
hubs include electronics to regenerate and retime the signal between each hub
port. Others act as signal splitters, similar to the multi-tap cable-TV splitters you
might use on your home antenna coax. Some reroute the network signals to
each active device in series, other hubs redistribute received signals out all ports
simultaneously. However, all devices connected to a hub reside in the same
collision domain, meaning that their transmission behavior is governed by the
CSMA/CD mechanism to resolve contention for the use of the wire. This
precludes determinism and makes hubs impractical for use in real time control
In recent years hub technology has been supplanted by a newer high speed
switching techniques to allow traffic between any two ports on the switch to pass
through the switch with an extremely low latency in the order of microseconds.
This technology has been enabled by specialized hardware that can support a
very high bandwidth backplane within the device. The speed of the backplane is
typically greater than the sum of the speeds of the Ethernet ports on the device,
and can accommodate all of the ports running at full speed without collisions.
Furthermore, these devices are capable of buffering frames temporarily to handle
short-term contention for the same output port.
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Switches are descendents of bridges. Like traditional bridges, switches build and
maintain internal tables that map Ethernet addresses to ports. A packet received
on one port is rapidly “switched” to the appropriate output port. Each port on the
switch is its own collision domain, so collisions between devices attached to the
switch do not occur. Switches eliminate the bus architecture. A switch segments
a network into many parallel dedicated lines to produce a contentionless,
scalable architecture. The switch establishes a direct line of communication
between two ports and maintains multiple simultaneous links between various
ports. The switch uses the addressing information in each Ethernet frame to
forward data only to the port connected to the destination device. The switch
manages network traffic by reducing media sharing since traffic is directed only to
the segment for which it is destined.
There are two basic methods of switching:
Cut-through switching starts sending packets as soon as they enter a switch and
their destination address is read. The entire frame is not received before a
switch begins forwarding it to the destination port. This reduces transmission
latency between ports, but it can propagate bad packets and broadcast storms to
the destination port.
Store-and-forward switching buffers incoming packets in memory until they are
fully received and a cyclic redundancy check (CRC) is run. This reduces bad
packets and collisions that can adversely effect the overall performance of the
segment. However, the buffering adds latency to the processing time. The
latency increases in proportion to the frame size.
Some switches perform on both levels. They begin with cut-through switching,
and monitor the number of errors that occur. When that number reaches a
certain threshold point, they become store-and-forward switches. They remain
so until the number of errors declines, then they change back to cut-through.
This is known as threshold detection or adaptive switching.
Full Duplex Switch Operation
The use of active switches in full duplex mode further increases the determinism
of an Ethernet network. By sending and receiving information at the same time,
a full duplex 10 Mbit network effectively operates at 20 Mbit. A 100 Mbit network
effectively operates at 200 Mbit. These very high speed transmission rates
virtually makes concerns about Ethernet’s lack of determinism go away.
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Advanced switches support a virtual LAN (VLAN) feature that allows users to
configure the switch so that ports are subdivided into groups such that all packets
received on one port will be transmitted on a specified group of ports. The
receiving port and the group of transmitting ports constitute a VLAN. VLAN’s
may typically be overlapped within a switch, such that any one port may appear
on multiple VLAN’s. This feature allows the user a great deal of flexibility over
partitioning the ports on a switch into multiple overlapping collision domains.
IGMP snooping constrains the flooding of multicast traffic by dynamically
configuring switch ports so that multicast traffic is forwarded only to ports
associated with a particular IP multicast group. Switches that support IGMP
snooping "learn" which ports have devices that are part of a particular multicast
group and only forward the multicast packets to the ports that are part of the
Performance Limitations of Switches
Switches do have some performance limitations that may affect some
applications. If a switch experiences internal congestion due to message packets
on multiple input ports contending for transmission to the same output port, the
switch may drop packets, or it may force a collision back to the transmitting
devices so they back off long enough for the congestion to clear. The approach
taken depends upon the implementation chosen by the switch vendor. In either
case, a variable latency is inserted into the message stream. This is generally
not a problem for office applications, but may have profound impact on industrial
Ethernet media components are based on the IEEE 802.3 standard, which is
available to the public for a small fee. The open nature of Ethernet and its
phenomenal growth has encouraged many companies to enter the market and
build Ethernet media components such as hubs, switches, cables, connectors,
and assorted network monitoring and maintenance tools. This competition in turn
has placed downward pressure on the cost of “off-the-shelf” Ethernet technology
to the end user.
However, for networked devices in an Industrial Automation application, the cost
of Ethernet connectivity is influenced by additional factors. Industrial network
products need to be built to withstand higher ranges of temperature, humidity and
electrical interference than most typical commercial “off-the-shelf” Ethernet
products were ever designed to handle. They should have been designed and
tested for compliance to the rigorous environmental standards typical for
industrial control devices (industrial CE mark, shock, vibration, etc.).
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Additionally, industrial Ethernet device interfaces usually include not just the
Ethernet interface hardware (transceiver, controller), but also include a high-
speed microprocessor, substantial RAM memory, ROM memory (EPROM or
Flash), and other components required to support the application interface. An
operating system, TCP/IP protocol stack and application software are typically
embedded in the ROM memory on the interface. The embedded software
handles all Ethernet-TCP/IP communications as well as interfacing to the
The strict environmental qualifications, complex hardware and embedded
firmware result in a communications interface that is more complex and
expensive than a typical off-the-shelf $50 Ethernet Network Interface card.
Advantages of Ethernet for Control
Wide Acceptance – Ethernet is an established, worldwide standard with support
from IEEE and the International Standards Organization. In addition to this
support from standards organizations, Ethernet has been broadly used in both
industrial and office environments. The high number of users has, in turn,
ensured the downward price of Ethernet components. Plus, IS and IT
departments worldwide have been using Ethernet for years. Such long-term
exposure to the Ethernet technology has produced an expansive knowledge
base and unparalleled resources.
Speed – Recent developments in Ethernet technology include Fast Ethernet and
Gigabit Ethernet. Fast Ethernet (100 Mbps/sec) provides a wire speed that is 10
times as fast as traditional Ethernet, which benefits bandwidth-hungry
applications, as well as the transfer of large data files over the network. Gigabit
Ethernet is an emerging technology that is basically Ethernet operating at 1000
Integration with Internet/Intranet – All installed Ethernet networks support one
or more communications protocols that run on top of Ethernet and provide
sophisticated data transfer and network management functionality. Of these,
TCP/IP is receiving the most attention due to the global Internet (including the
World Wide Web) and the corporate Intranets that are transforming how
corporations distribute information today. Many believe that using Ethernet
(especially if the organization dabbles in e-commerce) at all levels in the factory
will help integrate and optimize the flow of information from the shop floor to the
Broadcast/Multi-cast Traffic - I/O traffic will not typically pass through a router.
By design, the Time-To-Live parameter (see Internet Protocol for details of TTL
parameter) is configured for a value of 1. This value will be decremented by any
router and then discarded. A value of 1 is selected to avoid attempts to
implement I/O control (high-speed) through a slow network device (router) or
through a slow network.
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Broadcast/Multi-cast Traffic - Although switches isolate separate collision
domains on each port, they do not create separate broadcast domains.
However, each VLAN is a separate broadcast domain, if this feature is enabled
on the switch. An Ethernet broadcast message that is received on any port will
be re-transmitted on all switch ports, to all attached devices. This means that
switches do not eliminate the problem of excessive broadcast traffic that can
cause severe performance degradation across an entire Ethernet network when
a damaged or improperly configured device is attached to the network. Some
switch vendors are working on proprietary methods for suppressing excessive
broadcast messages in their switches, but this is not universal. Broadcast
messages are common on Ethernet networks that carry the TCP/IP protocol
because Ethernet broadcast messages are used by TCP/IP for address
resolution. However, broadcast traffic represents a small percentage of network
traffic on a network that is properly configured and operating normally.
Deterministic Data Delivery – In applications with sensitive timing, a single
message received later than anticipated can shut down the process, resulting in
lost production or even damaged goods and equipment.
Active Components – Using Ethernet for control increases the number of failure
points in a system due to the need for active components. Switches, repeater
and hubs are active devices, containing complex digital circuitry and requiring
power (AC in most cases) to operate. The failure of a switch or hub will
effectively cause a communications failure for all of the devices attached to that
device’s ports, including other hubs or switches that may be attached to one or
more ports of the failed device. The devices attached to the failed hub or switch
will be unable to communicate with the rest of the plant network until the switch is
replaced or repaired.
Security - It is essential that the factory control network be isolated from the
corporate IT network and that unauthorized access be prohibited. Broadcast
storms, network upgrades, and activities by IT personnel can also severally
impact the operation of the control network.
Lack of an application layer standard – Ethernet technology provides a set of
physical media definitions, a scheme for sharing that physical media and a
simple frame format and addressing scheme for moving packets of data between
devices. The TCP/IP protocol suite provides a set of services that two devices
may use to communicate with each other over an Ethernet LAN. However,
TCP/IP does not guarantee effective communicate or interoperability. A standard
application layer is a necessity for universal interoperability over Ethernet-
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Ethernet as a Control Network
One of the most common arguments that traditionally has been used against the
use of Ethernet for control is that Ethernet is non-deterministic. Determinism
enables users to accurately predict data transmission and guarantee its arrival at
the same time every time (or to quickly recognize that it did not arrive and take
appropriate action). The improvements in Ethernet technology mentioned earlier
in this article have improved the determinism and performance of Ethernet to a
great extent. Switches break up collision domains into single devices or small
groups of devices, effectively reducing the number of collisions to almost zero.
CSMA/CD provides the collision mechanism for detecting and recovering from
contention for the network when it does occur. Furthermore, there are efforts in
place to create a prioritization scheme for messages over Ethernet (IEEE 802.1p)
that if implemented inside switches could potentially be used to prioritize
control/alarm message packets over programming/data packets on Ethernet.
However, all of these are untried technologies in high-speed control applications.
In many applications with sensitive timing, a single message received later than
anticipated can shut down the process, resulting in lost production or even
damaged goods and equipment. Variable packet latency or dropped packets
within Ethernet switches could potentially cause this to happen. Losing a hub or
switch in an information-only application will result in lost production data; losing
one in a control application can result in lost production and possible damage to
the production equipment itself. These and other issues must be resolved in
order to rationally determine the types of control applications for which Ethernet-
TCP/IP technology is a good or even an acceptable solution.
Security can be implemented by providing a “firewall,” which denies access to
anyone who does not have an authorized IP address to access the network.
Special security software is also available. Because broadcast storms
(excessive transmission of broadcast traffic), network upgrades, and other
activities by IT personnel can several impact the operation of the control network,
IT personnel must be well informed and trained in the special requirements of
Most importantly, the lack of a standard application layer has been partly
resolved with the introduction of industrial automation oriented protocols like
EtherNet/IP, IDA, ProfiNet, etc.
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The global acceptance of Ethernet-TCP/IP has made it a popular choice for many
end users and for a wide variety of network applications. It offers an abundance
of compatible products and a high data throughput at a relatively low cost. As
end users begin looking to expand Ethernet’s responsibilities on the plant floor,
they should consider the following:
• Can the number and types of devices in the system, the frequency of data
exchanges, and the sizes and types of data packets on the wire be managed
in order to deliver an acceptable level of performance and determinism for the
• Can information and control messages be successfully mixed on the same
• Is there a reliable source of power available for all active media components?
• Will the application be adversely affected by Ethernet’s complex rules
regarding cable lengths and configuration, and the increased number of
failure points in a system due to the need for active components such as hubs
• Will the devices required to solve the application interoperate, or does each
vendor use their own application level protocol?
• Does the application require fully redundant media?
• Do all of the devices and media components meet the environmental
specifications and agency approvals required for the application (such as
temperature, humidity and vibration)?
• Who will install, manage and maintain the Ethernet network?
• Is the plant floor environment electrically noisy, and how will that impact the
performance of the Ethernet network?
• Is the cost per connection point acceptable for the application?
Many of these questions are common to all industrial automation networks and
are not unique to Ethernet alone, but Ethernet-based solutions must address
them. Ethernet has a bright future in industrial automation applications.
However, care must be taken that it is carefully applied to applications for which
its features and limitations are a good match.
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